1. Field of the Invention
The present invention relates to a thermoplastic resin composite, particularly a resin composite comprising a polyamide and polyolefines, which is low in water absorption and superior in dimensional stability, rigidity, toughness and moldability. The thermoplastic resin composite of the present invention finds wide applications in mechanical parts, automobile parts, electric or electronic parts, etc.
2. Description of Related Art
Polyamide resins, being well balanced in mechanical properties, heat resistance, chemical resistance and moldability, find wide applications in electrical or electronic parts, automobile parts, etc. However, the polyamide resins are prone to absorb moisture. Upon the absorption, the polyamide resins show large dimensional change and large reduction in mechanical properties such as bending strength, modulus of elasticity and the like. Accordingly, the polyamide resins are not suitable in parts requiring dimensional accuracy, and their improvement is desired.
On the other hand, polypropylene is lightweight, low in water absorption, superior in melt flowability, and low in cost, and is used in a large amount in automobile parts and electrical parts. However, polypropylene has insufficient heat resistance, strength and rigidity. Polypropylene tends to crystallize and has a large mold shrinkage coefficient so that upon molding, dimensional accuracy is limited. Hence, polypropylene may per se have limited applications.
In order to improve the dimensional change of polyamide caused by water absorption, it was proposed to introduce a monomer unit into the main chain of polyamide by copolymerization, and the monomer units consisting of an aromatic dicarboxylic acid, an aromatic diamine or a salt thereof by copolymerization. Alternatively, a polyamide may be blended with a polymer having low water absorption. The polymer having low water absorption includes crystalline resins and synthetic rubbers, which may be made of one of polypropylene modified by an unsaturated carboxylic acid or a derivative thereof, ethylene, and a copolymer having the propylene units and ethylene units.
For example, Japanese Patent Application Kokai (Laid-Open) No. 12546/1967 discloses a thermoplastic resin composition comprising 50-99% by weight of a polyamide and 50-1% by weight of an unsaturated carboxylic acid-olefine copolymer, which has improved compatibility. The resin composition has excellent mechanical properties, particularly excellent rupture property but does not satisfy all of low water absorption, rigidity and heat resistance.
Japanese Patent Publication No. 30945/1970 discloses a method of manufacturing a resin composition comprising an olefine polymer, a polyamide and/or a polyester, and a polyolefine modified with at least one of acids, esters, amides, acid anhydrides and epoxy group. The resin composition has satisfactory dispersion and is suitable for use in fibers. However, upon injection molding or extrusion, the composition shrinks, thereby the molded article having inferior dimensional accuracy and insufficient impact resistance.
Japanese Patent Application Kokai (Laid-Open) No. 262853/1985 discloses a polyamide resin composition comprising a polyamide and a modified ethylene-propylene block copolymer, which has low water absorption. In the resin composition, the water absorption of polyamide is reduced to a certain extent without significantly sacrificing its rigidity and heat resistance. However, the water absorption level of the resin composition is still insufficient.
Japanese Patent Application Kokai (Laid-Open) No. 223250/1987 discloses a resin composition obtained by kneading a crystalline polyolefine with a polyamide and an unsaturated carboxylic acid derivative and further kneading the resulting modified polyolefine with a polyamide and a polyolefine. The resin composition has low water absorption, excellent tensile strength and excellent surface gloss. The resin composition, however, does not satisfy both of rigidity and impact resistance.
Japanese Patent Application Kokai (Laid-Open) No. 223251/1987 discloses a resin composition having excellent impact resistance, obtained by adding, to the above resin composition, an ethylene-.alpha.-olefine copolymer of low crystallinity. The resin composition has improved water absorption, but has low rigidity and does not satisfy both of low water absorption and mechanical properties.
The above-mentioned Japanese Patent Application Kokai (Laid-Open) No. 223250/1987 also discloses a resin composition comprising a crystalline polyolefine, a polyamide and a small amount of a crystalline polyolefine modified by an unsaturated carboxylic acid. The resin composition, however, does not satisfy all of low water absorption, rigidity and impact resistance.
Japanese Patent Application Kokai (Laid-Open) No. 51458/1989 discloses a polyamide resin composition comprising a polyamide resin, a crystalline polypropylene modified by unsaturated carboxylic acid and an ethylene-.alpha.-olefine copolymer modified by an unsaturated carboxylic acid. The polyamide resin composition gives a small dimensional change upon water absorption and has excellent rigidity and impact resistance. The polyamide resin composition, being rich in the polyamide component, has excellent mechanical properties, but is still insufficient in water absorption and does not fully satisfy both of low water absorption and mechanical properties.
Japanese Patent Application Kokai (Laid-Open) No. 87652/1989 discloses a polypropylene resin composition having excellent impact resistance, comprising a partially modified crystalline propylene-ethylene block copolymer, a polyamide and a modified ethylene-.alpha.-olefine copolymer. The composition contains a polypropylene as a matrix and a polyamide as a dispersed phase, thereby having improved heat resistance and mechanical properties as compared with the polypropylene. However, the compositions has significantly inferior rigidity and heat resistance as compared with the polyamide.
Japanese Patent Application Kokai (Laid-Open) No. 146942/1989 discloses compositions each comprising 40-60% by weight of a modified polyolefine copolymer grafted with an unsaturated carboxylic acid or a derivative thereof and 60-40% by weight of a polyamide. In these compositions, the incorporation of the modified polyolefine of relatively high molecular weight having an melt flow rate of 2.0 g or less per 10 minutes improves the rigidity, water resistance and weld strength. However, the compositions do not improve impact resistance; the mold shrinkage coefficient is high; the dimensional stability upon molding is low; and the melt does not sufficiently flow.
Japanese Patent Application Kokai (Laid-Open) No. 91560/1991 discloses a polyamide resin composition comprising 100 parts by weight of polyamide, 1-100 parts by weight of a modified polyolefine, 5-250 parts by weight of a polypropylene resin, 0.01-3.0 parts by weight of an organic heat stabilizer and 0.1-5.0 parts by weight of a particular carbon black. The polyamide resin composition does not age much upon heating. The polyamide resin composition, however, has insufficient impact resistance and dimensional stability upon molding.
Japanese Patent Application Kokai (Laid-Open) No. 109452/1991 discloses a resin composition comprising 10-89.9 parts by weight of a polypropylene resin, 10-89.9 parts by weight of a polyamide, 0.1-5 parts by weight of an unsaturated carboxylic acid-modified polyolefine, 0-30 parts by weight of an impact improver and 0-60 parts by weight of a reinforcing agent, wherein the resin composition is 100 parts by weight. The resin composition shows excellent toughness, rigidity and heat deformation stability, but has insufficient melt flowability during molding and insufficient lightweightness.
Japanese Patent Application Kokai (Laid-Open) No. 115342/1991 discloses a resin composition comprising 94-50% by weight of a polypropylene, 1-40% by weight of a modified polyolefine and 5-40% by weight of a polyamide, wherein the ratio of the melt viscosity of the polyamide to the melt viscosity of the polypropylene is 1 or more. The resin composition has improved heat resistance as compared with the polypropylene, but has no sufficient improvement in dimensional stability upon molding and rigidity.
Japanese Patent Application Kokai (Laid-Open) No. 146552/1991 discloses a resin composition comprising 40-80% by weight of a polyamide, 1-40% by weight of a modified polyolefine and 20-60% by weight of a polypropylene. The resin composition shows excellent coating property by having a melt viscosity ratio .eta..sub.pp /.eta..sub.PA of 0.75 or more at a shear rate of 3,500 sec.sup.-1 at the molding temperature, but is insufficient in impact resistance and dimensional stability upon molding.
Japanese Patent Application Kokai (Laid-Open) No. 207735/1991 discloses a resin composition comprising a polyamide, a polyolefine and a modified polyolefine. The modified polyolefine having a tensile yield strength of 300 kg/cm.sup.2 or more improves mechanical properties, particularly, weld strength of a molded article made of the resin composition. However, the resin composition has high shrinkage coefficient upon solidification during molding, thereby the molded article having insufficient dimensional stability and rigidity.
Japanese Patent Publication No. 44108/1980 discloses a multi-phase thermoplastic resin composition having a polyamide matrix and particles dispersed therein. The particles are made of a polymer having at least one residue selected from ethylene, carbonyl compounds, .alpha.,.beta.-unsaturated carboxylic acids and derivatives thereof, unsaturated epoxides, carboxylic acids and derivatives thereof, acrylic acid esters, monomers having aromatic side chains and unsaturated carbon-carbon monomers. The resin composition has excellent impact resistance and modulus of bending elasticity. However, the resin composition is insufficient in low water absorption; the resin composition does not have both mechanical properties and dimensional stability upon water absorption.
Japanese Patent Application Kokai (Laid-Open) No. 9661/1980 discloses a thermoplastic resin composition having flexibility, comprising (a) a modified ethylene copolymer grafted with 0.05-1.5% by weight of an .alpha.,.beta.-unsaturated carboxylic acid or a derivative thereof and (b) a polyamide at a ratio of 2/3:1 to 6:1. The thermoplastic resin composition has improved flexibility and impact resistance but has reduced rigidity and elongation upon rupture.
Japanese Patent Application Kokai (Laid-Open) No. 123158/1979 discloses a polyolefine resin composition comprising: a polyolefine resin, including an unsaturated carboxylic acid-added polyolefine resin; a nitrogen-containing resin; and a filler. The polyolefine resin is superior in mechanical properties, heat resistance and coating property. The resin composition has improved bending strength, heat deformation temperature and coating property. However, the resin composition has problem in rigidity, toughness, lightweightness and dimensional stability.
Japanese Patent Application Kokai (Laid-Open) No. 232135/1984 discloses a polyolefine resin composition superior in dyeing property, comprising a modified polyolefine, a polyamide and a crystalline polyolefine, wherein the amount of the olefine units is 70% by weight or more of the total. The incorporation of a large amount of polyolefines improves, upon injection molding, mechanical strength, rigidity, heat resistance, etc. However, the extent of improvement is limited.
Japanese Patent Application Kokai (Laid-Open) No. 118735/1985 discloses a resin composition with both mechanical properties and low water absorption, comprising a polyamide and a modified polyolefine. The resin composition, however, is insufficient in balance between rigidity and low water absorption.
Japanese Patent Application Kokai (Laid-Open) No. 8246/1982 discloses a resin composition comprising a polyamide, a polyolefine having a crystallinity of 40% or more and a modified polyolefine obtained by modifying an ethylene-.alpha.-olefine copolymer having a crystallinity of 35% or less with an .alpha.,.beta.-unsaturated carboxylic acid or a derivative thereof. The resin composition has improved impact resistance and appearance, but has no sufficient balance between rigidity and low water absorption.
Japanese Patent Application Kokai (Laid-Open) No. 149940/1984 (Japanese Patent Publication No. 42109/1990) and Japanese Patent Application Kokai (Laid-Open) No. 110740/-1985 (Japanese Patent Publication No. 42379/1990) disclose a polypropylene composition comprising a polypropylene, a polyamide and a modified propylene-.alpha.-olefine copolymer, which has excellent rigidity, impact resistance, gloss and heat resistance. The resin composition has a polypropylene matrix, thereby considerably low rigidity expressed by modulus of bending elasticity, as compared with a polyamide matrix.
As described above, conventional polyamide resin compositions are not well balanced between the properties possessed by a polyamide and the properties possessed by a polyolefine. The polyamide has favorable properties such as the mechanical properties, heat resistance and moldability, and the polyolefine has favorable properties such as the lightweightness and low water absorption. Neither the polyamide nor the polyolefine has low warpage upon molding, good dimensional stability and good impact resistance.